Latest: Tuesday night's vote defeats showed the Government has effectively lost its Parliamentary majority, a spokesman for Jeremy Corbyn said.
Defeat in the meaningful vote would be a "major blow to the Government's credibility and ability to govern", he added.
He said: "We have talked to other parties about ensuring this absolutely terrible deal that has been signed by the Government is defeated in Parliament and that the no-deal option is not available and is blocked, and I think we are making some progress with that."
He went on: "The prospect of this agreement passing in Parliament have, I would say, receded.
"Some of the figures of the scale of the Government's likely defeat are exaggerated, but at the moment it clearly looks like it is not going to pass."
The Prime Minister said the EU would not want Britain to be in a backstop for "longer than is necessary".
She told MPs: "I recognise there are concerns about the backstop but it is indeed the case that it is not attractive for the European Union to have the United Kingdom in the backstop for a number of reasons.
"First of all because in that backstop we will be making no financial obligation to the European Union; we will not be accepting free movement; and there will be very light-touch level playing field requirements.
"These are matters which mean that the European Union does not see this as an attractive place for them to put the UK: they think that's an attractive place for the UK to be in and they won't want us to be in it for longer than is necessary."
Mrs May said the Government would not revoke Article 50, after she was asked about the legal opinion of the ECJ's advocate-general Manuel Campos Sanchez-Bordona during PMQs.
She said: "If his determination does go ahead, what it says is that it is possible for a country unilaterally to revoke Article 50, but that isn't about extending Article 50 - it's about making sure that we don't leave the European Union...
"We will not revoke Article 50: the British people voted to leave the European Union and we will be leaving."
DUP deputy leader Nigel Dodds said: "It is clear from the Attorney General's advice on the legal effect of the protocol on Northern Ireland to the Prime Minister and her Cabinet colleagues that we were right to advocate its full publication and we have been vindicated in our opposition to the backstop arrangements contained within the Withdrawal Agreement.
"This advice concisely sets out the stark reality of the operation of the backstop. Its publication demonstrates how the Prime Minister has failed to abide by the commitments she gave in that the United Kingdom as a whole would leave the European Union and that she would ensure there would be no customs or regulatory divergence within the United Kingdom.
"This backstop is totally unacceptable to unionists throughout the United Kingdom and it must be defeated and arrangements renegotiated that uphold the commitments which the Prime Minister and her Government has made in the House of Commons."
Mrs May also faced accusations from the DUP that the backstop had been based on a "false assertion" and asked why she had allowed the EU to use it as a "negotiating ploy".
The Prime Minister said it was not a negotiating ploy, explaining: "What it is is our commitment as a UK Government to the people of Northern Ireland."
She added: "People need to know it is beyond a political assertion that there is that commitment there to the people of Northern Ireland to ensure that we have no hard border."
Latest: Attorney General Geoffrey Cox's full legal advice to the Cabinet on Brexit reveals "central weaknesses in the Government's deal", shadow Brexit secretary Keir Starmer has said.
Mr Starmer said he had seen the full document, which is due to be released on Wednesday following Tuesday's parliamentary vote which found the Government in contempt of Parliament.
Writing on Twitter, Mr Starmer said: "Having reviewed the Attorney General's legal advice, it's obvious why this needed to be placed in the public domain.
"All week we have heard from Government ministers that releasing this information could harm the national interest. Nothing of the sort. All this advice reveals is the central weaknesses in the Government's deal.
"It is unthinkable that the Government tried to keep this information from Parliament - and indeed the public - before next week's vote."
Having reviewed the Attorney General’s legal advice, it’s obvious why this needed to be placed in the public domain. 1/3— Keir Starmer (@Keir_Starmer) December 5, 2018
Green MP Caroline Lucas tweeted sections of the legal advice, which she said suggested it was not received by the Cabinet until November 13 - the day MPs first voted for it to be released.
Ms Lucas highlighted concerns in the document that the protocol setting out the backstop arrangements for Ireland would "endure indefinitely".
There seem to me to be three key paragraphs in the Attorney General's legal advice to the Prime Minister on the Protocol on Ireland/Northern Ireland - the 'backstop - in the Withdrawal Agreement.
Here they are. 1/4
Para 16: The Protocol will "endure indefinitely". pic.twitter.com/UX7ZfClGob— Caroline Lucas (@CarolineLucas) December 5, 2018
According to the extracts, she said, a review mechanism in the Brexit deal "does not provide a unilateral route out of the backstop" and there is "a legal risk that UK could become stuck in protracted and repeating rounds of negotiations".
The legal advice was posted on Twitter by several MPs, including Ms Lucas and Mr Starmer, ahead of publication.
In its conclusion, it says: "In the absence of a right of termination, there is a legal risk that the United Kingdom might become subject to protracted and repeating rounds of negotiations.
"This risk must be weighed against the political and economic imperative on both sides to reach an agreement that constitutes a politically stable and permanent basis for their future relationship.
"This is a political decision for the Government."
And the *really* weird thing is that the date on the Attorney General's advice suggests that the Cabinet did not get any formal legal advice from him before 13 November - the day MPs first asked for it to be published ... 🤔 4/4 #Brexit #Art50 pic.twitter.com/88ZY8Dju31— Caroline Lucas (@CarolineLucas) December 5, 2018
Another section says that as currently written, the backstop "does not provide for a mechanism that is likely to enable the UK lawfully to exit the UK-wide customs union without a subsequent agreement".
It adds: "This remains the case even if the parties are still negotiating many years later, and even if the parties believe that talks have clearly broken down and there is no prospect of a future relationship agreement.
"The resolution of such a stalemate would have to be political."
Update: Theresa May’s Brexit deal will face fresh scrutiny when the Cabinet’s full legal advice is published, following one of the most punishing days in the Commons for a sitting UK government in recent memory.
Commons Leader Andrea Leadsom said the advice on the Withdrawal Agreement from Attorney General Geoffrey Cox would be published on Wednesday morning, after MPs on Tuesday found the government to be in contempt of parliament for the first time in modern history.
Wednesday is the second of five days of debates on the deal before the December 11 vote, and follows a first day which saw a series of dramatic defeats for the British Prime Minister’s struggling administration.
As well as losing the contempt vote, the government was also forced to allow MPs to have a say in what happens next if the Brexit deal is voted down on Tuesday.
Mrs Leadsom told BBC Radio 4’s Today programme that the government would release the legal advice, but “not without some regret”.
She also fired a warning shot at rebels within the Tory Party, saying: “Going forward, not only will government ministers be very careful about what they ask law officers to give advice on, but law officers themselves will be very reluctant to give any advice to government that they might then see published on the front pages of the newspapers, so it’s the principle of the thing.
“And, frankly, I think any parliamentarian who wants at some point in the future to be in government is going to live to regret their vote last night.”
Mrs Leadsom, who had been reported to have been leading intra-cabinet attempts to get Mrs May to change the deal agreed with Brussels after months of hard-fought negotiations.
Synchronise watches everyone: Andrea Leadsom says the full Brexit deal legal advice will be published at 11.30am.— David Wilcock (@DavidTWilcock) December 5, 2018
She told Today that she was staying in government to make “absolutely sure” Britain does not end up in the backstop, saying: I am a very strong arch Brexiteer, I genuinely believe that we have a bright future ahead of us when we leave the EU.
“And so all the way through I’ve had conflicting thoughts and I’ve had to consider whether I can live with things, but at the end of the day this deal is the best combination that we’re going to get and so I just urge colleagues to look at it carefully to give it a real chance.”
Theresa May’s Brexit deal was likened to Frankenstein’s monster – “an ugly beast that no-one voted for” – as MPs concluded the first of five days of debate on the British Prime Minister’s exit plan.
Labour former minister David Lammy roused MPs with a late-night commons speech in which he quoted Churchill and Shakespeare and accused Brexiteers of wanting to establish “Empire 2.0”.
The comments came at the end of a torturous day for the British government in which it suffered three humiliating Commons defeats in little more than an hour.
Commons leader Andrea Leadsom was first forced to agree to publish the government’s full legal advice on the deal after MPs found the government in contempt of Parliament and then MPs succeeded in a bid to grant the commons a greater say over what happens if Mrs May’s deal is rejected next Tuesday.
Mr Lammy, rising to criticise the deal, said: “Let us now be honest with the country, total independence is a fantasy, it’s the same idea that motivates an angry teenager to run away from their family, total independence means throwing a tantrum and ending up in the cold.”
The Tottenham MP said many Brexiteers were “still mourning Suez”, he said: “When those on the other side of this debate say that they want ‘Empire 2.0’, let us ask what does that mean? What was imperialism, what was colonialism?
“At its worst the British Empire was exploitation and subjugation, moral superiority that led to putting humans in shackles, the oppression of black and brown people because this country thought it knew best, those countries once coloured pink on the globe were not won in negotiations, they were taken by force. Today we need to build a new image of Britain, one that brings this country together after years of division.”
House of Commons votes 311 to 293 to approve the privilege motion, finding Ministers in contempt and ordering the immediate publication of the full legal advice on the #Brexit deal. pic.twitter.com/haXVmbH36s— UK House of Commons (@HouseofCommons) December 4, 2018
Mr Lammy concluded by saying Brexit was a “historic mistake”, adding: “This country is crying out for a second chance, 700,000 people marched on the streets of London, millions more campaigned online and wrote to their MPs. They are asking for one thing: an opportunity to right the wrong of 2016, another shot at the imperfect but audacious European dream or as Shakespeare put it in Richard II from John of Gaunt, ‘this England that was wont to conquer others has made a shameful conquest of itself’.”
DUP MP Paul Girvan also stirred the chamber when he suggested Mrs May’s Brexit deal would do what the IRA failed to do and lead to the reunification of Ireland.
He said: “Many families from this United Kingdom gave sons to fight for what we have in Northern Ireland, which is to remain part of the UK.
“What was not achieved by the IRA and Republicanism has been achieved by those bureaucrats within Europe and with a pen potentially leaving Northern Ireland on the route to a united Ireland.”
Stephen Barclay, in his first speech from the despatch box as Brexit Secretary, said Mrs May’s deal was “not perfect” but said: “It recognises our shared history and values and provides a framework for our future economic and security relationship.”
He added: “This deal is a choice between the certainty of continued cooperation or the potentially damaging fracture of no-deal.”
MPs are expected to resume the debate on Mrs May’s Brexit deal early this afternoon.
- Press Association